Although the present invention is particularly well adapted for turboprops of a civil or military airplane, without propeller fairing, it is in no way limited to this latter application.
It is known that turboprops without propeller fairing of an airplane, in addition to the thrust component, apply normal stresses to the rotation axis of the propeller, contrary to airplane turbojets. Such normal stresses, commonly referred to as loads 1P in the aeronautical language, occur when the air flow upstream the propeller of turboprops has a not nil incidence with respect to the rotation axis of the propeller (the air aerodynamic speed vector is not co-linear to said rotation axis). They may be very important (for example several times higher than the thrust stresses) depending on the flight phase and the configuration of the airplane.
It is further known that the propeller incidence and sideslip of an airplane turboprop, as well as the speed of the airplane, are parameters impacting on the intensity of loads 1P. In particular, the higher the incidence and the speed, the more important the ratio of the loads 1P produced on the thrust as developed by the propeller.
Thus, the loads 1P could be assimilated to the work of an airplane aerofoil and, depending of the flight phases and the configuration of the latter, become added or, on the contrary, disturb the work of the other aerofoils of the airplane (aerofoil, horizontal stabilizer, vertical stabilizer). Therefore the effect of the loads 1P impacts:                on the controllability and the stability of the airplane. Depending on the configuration of the airplane and the flight phase, the loads 1P could be either stabilizing, in which case the maneuverability of the airplane is reduced, or destabilizing, in which case they should be counteracted so as to restore an acceptable behaviour of the airplane. Any way, this results in the stabilization and control surfaces being increased so as to counteract such stresses;        on the performance of the airplane. The indispensable increase of the stabilization and control surfaces generates an additional drag. Furthermore, for stabilizing the airplane, it is sometimes necessary to provide an antagonistic work to that developed by loads 1P, leading in an additional loss of energy; and        on the mass of the airplane. The structure of the airplane is sized so as to withstand such high loads 1P while the latter do not produce any useful work for the airplane mission.        